In groundwater studies, hydrologic data obtained from production wells are often used to describe and simulate regional groundwater conditions. Production wells commonly are perforated over long intervals and yield groundwater from more than one water-bearing zone or aquifer. Determining which water-bearing zone particular data represent, as well as determining the area distribution for that data and the change of data over time, may be impossible using indirect information such as well construction data, geophysical logs from long-screened production wells, and composite water-chemistry samples from well surface discharge. Currently available equipment for obtaining information on the velocity distribution and entry of water into a well bore includes vertical-flow impeller-type flow meters, and heat pulse, electromagnetic, video camera, and sonic geophysical tools. These existing tools are commonly three to six feet in length and have diameters greater than two inches. As a result, these devices cannot be used in wells that have small entry tubes or restricted space within the well. Further, these devices cannot negotiate bends which are commonly encountered in production wells. Many of these tools also have upper and/or lower limits to the range of flow rate that they can determine, and these limits handicap their use in determining the wide range of discharge rates found in monitoring and production wells. Well bore velocity may vary greatly within a well, and may not be known until at least one test has been made. Then it might be necessary to change a tool and retest.
Depth dependent data, obtained from observation wells which are perforated over specific intervals, can be used to directly determine the water level, water chemistry, and aquifer properties of individual water-bearing zones. However, such wells are expensive to construct, and provide data only for selected water-bearing zones that may not be representative of the remainder of the aquifer. Currently available equipment for such purposes include wire line, bailer, and downhole samplers. Many of these tools are also of a size that limits there access into production and monitoring wells.